welcome to GoY.
is this from bird seed? does look a little bit like an Artemisia. Are they flowers that are forming , like green candles?
is it aromatic when you crush a leaf?

I'd say Artemisia too, Seaburn. It has a lovely smell and is frequently seen growing wild on roadsides.

It looks like common ragweed, to me.

not heard of that so I've looked it up and I do believe you are right tug.
botanical name is Ambrosia artemisiifolia the species name means leaves like an Artemisia.
Native to America - wonder what it is doing here :o) probably from bird seed.

it is a cause of hayfever syptoms apparently

Not a normal component in bird seed, but it might have been a weed in the field where one of the components was grown.